1. Technical Field
The present invention relates to an air separator for a gas turbine, which has a structure capable of preventing cracks at the air separator end portion and distributing cooling air homogeneously to a plurality of first stage moving blades.
2. Description of Related Art
An air separator for a gas turbine is a device for guiding cooling air for a rotor and moving blades from a compressor. FIG. 8 is a section of an air separator for a prior art gas turbine, and FIG. 9 is a perspective view. In FIG. 8, reference numeral 1 designates a rotor, and numeral 2 designates a first stage moving blade mounted on the rotor 1 through a disc portion 7 so that it rotates together with the rotor 1. Numeral 3 designates a first stage stator blade, and numeral 4 designates a seal ring retaining ring inside of the stator blade 3. Numeral 5 designates a duct for guiding cooling air 30 from a compressor into a space 6. The numeral 7 designates the aforementioned disc portion on which the root of the moving blade 2 is mounted, and numeral 8 designates bolts/nuts. Numerals 41 and 42 designate seal portions on the stationary side, and numeral 43 designates air feed holes for feeding the cooling air to the downstream stage of the disc portion 7.
Numeral 10 designates an air separator which is formed into a cylindrical shape surrounding the rotor 1 and which has a flange portion 13 on its lefthand side and bolt holes 9 formed so that the air separator is mounted on the rotor 1 by the bolts/nuts 8. The air separator 10 has such a flange portion 12, which on its righthand side contacts with the disc portion 7 around its leading end portion. An air hole 11 is formed around the central portion of the air separator 10 for guiding the cooling air 30 from the space 6 via a passage 31, which is formed between the rotor 1 and the inner circumference of the air separator, into the air feed holes 43 of the disc portion 7 and further into radial holes 44 for guiding the air from the disc portion 7 to the first stage moving blade 2. On the other hand, the outer circumference of the air separator 10 is close to the seal portions 41 and 42 on the stationary side to prevent the cooling air from leaking to the outside through seal fins.
FIG. 9 is a perspective view of the air separator 10. This air separator 10 is formed into a cylindrical shape surrounding the rotor and has the numerous air holes 11 around its central portion, as described above, and the flanges 12 and 13 at its two ends. Of these, the flange portion 13 is mounted on the rotor 1 by the bolts/nuts through the bolt holes 9.
FIGS. 10(a)-10(b) show the flange portion of the air separator on one side of the moving blade, FIG. 10(a) is a section through the contacting portion of the flange portion and the moving blade, and FIG. 10(b) is a perspective view showing a state in which cracks occur in the flange portion. As shown in FIG. 10(a), the leading end portion of the flange portion 12 is lightly held in contact with the disc portion 7 of the rotor while keeping a constant facial pressure with the disc side.
As described above, the air separator 10 has the overhang structure in which it is fixed at flange portion 13 on the side of the rotor 1 by the bolts/nuts 8. The flange portion 12 at the other end abuts under the constant facial pressure against the disc side so that it rotates together with the rotor 1. After repeated hot restarts, therefore, the flange portion 12 may develop have a crack, as shown in FIG. 10(b).
The cause for this crack will be described. If a restart is made in a hot state after being stopped for several hours, and if the cold cooling air is fed to cool the air separator 10, the separator 10 is abruptly cooled to lower the holding force of the flange portion 12 on the disc portion 7. If the run is made under this lowered holding force, a relative slip occurs between the flange portion 12 and the disc abutting side so that the surface is roughed to cause fine cracks due to local stress. These fine cracks gradually open so that the opened portion is torn up by the centrifugal force to cause the crack, as shown in FIG. 10(b).